go shopping 购物,本身就是一个词组,就像go swimming,去游泳一样.
它已经用助动词do修饰了.不过,还可以说成How often are you going shopping?
一进行时态（包括现在进行时和过去进行时）必须用be动词.如：
What are you doing,mum?
I was having tea with a friend at that time.
二固定词组 如：
be busy with be famous for be used to be related to等
三修饰形容词 be+adj.这时它是连系动词